Unnamed Occurrence (ARDF - MF007; northwest of Mt. Marchainville), Yakutat District, Skagway-Hoonah-Angoon Borough, Alaska, USA

Chugach terrane. The ilmenite locality and the nearby copper-stained sites are in Glacier Bay National Park and Preserve.
Location: The occurrence is at an elevation of about 2000 feet about 3 miles northwest of Mt. Marchainville, and 1.5 miles southeast of Finger Glacier. It is near the approximate center of section 24, T. 39 S., R. 50 E., of the Copper River Meridian. The location is accurate to about 0.1 mile based on transposition of Rossman's (1963) sample no. 40 to the topography of the 1961 edition of the Mt. Fairweather B-4 quadrangle. The location is the same as number 15 of Kimball and others (1978), and location 7 of Cobb (1972). MacKevett and others (1971, p. 52) cite Rossman for authority on copper-staining close to this location. The approximate location of copper-staining reported by MacKevett and others (1971--location 82) is about 0.25 mile southeast of the coordinate position.
Geology: The occurrence is within the Fairweather terrane of Brew and others (1978). It is in the southwest part of the Crillon-LaPerouse mafic-ultramafic body which is intruded into biotite and hornblende schist of the upper Chugach terrane of Berg and others (1972). At the occurrence, an ilmenite-rich layer in gabbro is approximately 50-feet thick. Its strike length is uncertain because of the extremely rough topography. Rossman (1963) determined X0.0 percent titanium by spectrophic analyses (sample 52A Rm g 40). The sample also contained X0.+ percent iron, but only 0.0X percent of copper, cobalt, or nickel. Ilmenite determined by weight in mineral separates ranged from 5 to 11.4 weight percent. A nearby copper (malachite-stained) occurrence is near or at the contact of the intrusion; possibly the occurrence represents oxidized cupriferous amphibolite schist at the contact.
Workings: No workings, surface outcrop only.
Age: Tertiary.
Alteration: Local iron-and copper-(malachite) staining.
Reserves: Possibly extensive deposits are suggested by the thickness (50-feet) and by several nearby ilmenite-rich occurrences.

Commodities (Major) - Fe, Ti; (Minor) - Cu
Development Status: No
Deposit Model: Possibly Bushveld Fe-Ti-V (Cox and Singer, 1986; model 3). Magmatic segregatio

References:
Berg, H.C., Jones, D.L., and Richter, D.H., 1972, Gravina-Nutzotin Belt--Tectonic significance of an upper Mesozoic sedimentary and volcanic sequence in southern and southeastern Alaska: U.S. Geological Survey Professional Paper 800-D, p. D1-D24. Brew, D.A., Johnson, B.R., Grybeck, D., Griscom, A., Barnes, D.F., Kimball, A.L., Still, J.C., and Rataj, J.L., 1978, Mineral resources of the Glacier Bay National Monument Wilderness Study Area, Alaska: U.S. Geological Survey Open-File Report 78-494, 670 p., 7 sheets. Cobb, E.H., 1972, Metallic mineral resources map of the Mount Fairweather quadrangle, AK: U.S. Geological Survey Miscellaneous Field Study Map MF-436, 1 sheet, scale 1:250,000. Cox, D.P., and Singer, D.A., eds., 1986, Mineral deposit models: U.S. Geological Survey Bulletin 1693, 379 p. Foley, J.Y., Light, T.D., Nelson, S.W., and Harris, R.A., 1997, Mineral occurrences associated with mafic-ultramafic and related alkaline complexes in Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 396-449. Kimball, A.L., Still, J.C., and Rataj, J.L., 1978, Mineral resources, in Brew, D. A., and others, Mineral resources of the Glacier Bay National Monument wilderness study area, Alaska: U.S. Geological Survey Open-File Report 78-494, p. C1-C375. MacKevett, E.M., Jr., Brew, D.A., Hawley, C.C., Huff, L.C., and Smith, J.G., 1971, Mineral resources of Glacier Bay National Monument, Alaska: U.S. Geological Survey Professional Paper 632, 90 p., 12 plates, scale 1:250,000. Rossman, Darwin, 1963, Geology and petrology of two stocks of layered gabbro in the Fairweather Range, Alaska: U.S. Geological Survey Bulletin 1121-F, p. F1-F50.